The regulation of signal transduction events following tissue injury is of prime importance in maintaining cell viability. This process is particularly relevant to diseases of the respiratory and cardiovascular system, where tissue insults such as ischemia, reperfusion, and sepsis are common. The applicants propose that this occurs through the involvement of the 90-kDa heat-shock protein hsp9O. Hsp9O is an abundant and ubiquitously distributed stress protein present in all living organisms from bacteria to man. Although hsp9O plays a role in steroid receptor maturation, and forms stable associations with several protein kinases, no clear picture regarding hsp9O's exact function at the molecular level has emerged. In this proposal, they hypothesize that hsp9O functions as a protein kinase chaperone, assisting in the correct packing of the regulatory and catalytic domains. By sequestering the catalytic subunits of a variety of protein kinases following injury, hsp9O could prevent both non-specific kinase denaturation/aggregation and the inappropriate activation of signal transduction pathways. In vivo cell culture experiments will be used to determine the identity and activity of protein kinases that interact with hsp9O following injury. In vitro protein biochemistry experiments will examine which kinase subfamilies contain members capable of interacting with hsp9O, and elucidate whether hsp9O plays a chaperone-like function in this interaction. Finally the mechanism of hsp9O kinase binding and release will be investigated using kinase mutants, domain- and loop-swapping constructs, and oriented peptide libraries, based on extrapolations from known protein kinase crystal structures.